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til/rails/prevent-mailer-previews-from-cluttering-database.md

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# Prevent Mailer Previews From Cluttering Database
ActionMailer Previews give you a way to view email templates that your system
sends. This is how I check that it is styled properly and that the logic and
data of the template are able to run and render.
Data for a preview typically means we need ActiveRecord objects and even their
associations. If we start creating one-off records in our previews either with
`#create` or with something like `FactoryBot`, those records will get left
behind in our development database. Every view and refresh of a preview will
generate more of these records.
One way to get around that is to use `#new` and `#build`. I've found this
cumbersome and it often leaves assocations missing or inaccessible.
What if instead the preview could clean up after itself? That sounds like a
great job for a database transaction.
Let's create a `test/mailers/previews/base_preview.rb` as a base class for all
our preview classes.
```ruby
class BasePreview < ActionMailer::Preview
def self.call(...)
message = nil
ActiveRecord::Base.transaction do
message = super(...)
raise ActiveRecord::Rollback
end
message
end
end
```
This wraps the existing `self.call` functionality in a transaction that
collects the resulting message from the preview and then rolls back the
database changes.
Now, instead of our individual preview classes inheriting directly from
`ActionMailer::Preview`, they can inherit from `BasePreview`.
```ruby
class UserMailer < BasePreview
# ...
end
```
[source](https://stackoverflow.com/a/31289295)